Nonexponential kinetics of a single tRNAPhe molecule under physiological conditions

The fluorescence decay functions of individual, specifically labeled tRNAPhe molecules exhibit nonexponential character as a result of conformational dynamics occurring during the measurement on a single molecule. tRNAPhe conformational states that interchange much more slowly are evidenced by the distribution of lifetimes observed for many individual molecules. A structural model for the nonexponential decay indicates that the tRNAPhe-probe adduct fluctuates between two states, one of which provides conditions that quench the probe fluorescence.

HPLC assay of acetylsalicylic acid, paracetamol, caffeine and phenobarbital in tablets

This paper present a HPLC method for simultaneous determination of acetylsalicylic acid, paracetamol, caffeine and phenobarbital in tablets, using chromatographic system consisting a Bio Rad 18 01 solvent pump, Rheodine 71 25 injector and Bio Rad 18 01 UV-Vis Detector. Separation was achieved using Bio SiL HL C18, 5 microm, 250 x 4.6 mm column. Mixture of acetonitrile-water (25:75 v/v) adjusted to pH 2.5 with phosphoric acid was used as a mobile phase at a flow rate of 2.0 ml min(-1). UV detection was at 207 nm range 0.01 AUFS. Under the same conditions it was possible to determine the level of salicylic acid. The chromatographic parameters such as retention times, capacity factor, peak asymmetry, selectivity factor and resolution factor was determined. The validation parameters: linearity (r > 0.998), intra-day precision (RSD: 0.36-1.89%) and inter-day precision (RSD: 0.58-2.18%), sensitivity (LOD: 9 x 10(-5)-1.7 x 10(-4) mg ml(-1) and LOQ: 2.5 x 10(-4)-5.6 x 10(-4) mg ml(-1)), accuracy (recoveries: 98.35-99.14%) and reproducibility (recovery values: 98.74-102.08% for acetylsalicylic acid, 99.93-102.11% for paracetamol, 98.25-102.12% for caffeine and 98.15-102.3% for phenobarbital) (RSD: 1.21-1.85%) were found to be satisfactory. The proposed HPLC method has been applied for the determination of acetylsalicylic acid, paracetamol, caffeine and phenobarbital in Malophenum tablets. The obtained RSD values were within 0.99-1.21%. The developed method is rapid and sensitive and therefore suitable for routine control of these drugs in dosage form.

HPTLC determination of ceftriaxone, cefixime and cefotaxime in dosage forms

The objective of this investigation was to develop a HPTLC method for the determination of ceftriaxone, cefixime and cefotaxime, cephalosporins widely used in clinical practice. High performance TLC of cephalosporins was performed on pre-coated silica gel HPTLC plates with concentrating zone (2.5 x 10 cm) by development in mobile phase ethyl acetate-acetone-methanol-water (5:2.5:2.5:1.5 v/v/v/v). A TLC scanner set at 270 nm was used for direct evaluation of the chromatograms in reflectance/absorbance mode. The calibration curves were established as dependence of peak height (linear and polynomial regression) and peak area (polynomial regression) versus ng level (125-500 ng for all cephalosporins investigated). Relative standard deviations obtained from calibration curves was compared. Precision (RSD: 1.12-2.91% (peak height versus ng) and RSD: 1.05-2.75% (peak area versus ng)), and detection limits (ng level) was validated and found to be satisfactory. The method was found to be reproducible and convenient for quantitative analysis of ceftriaxone, cefixime and cefotaxime in their raw materials and their dosage forms.

Theory of dust voids in plasmas

Dusty plasmas in a gas discharge often feature a stable void, i.e., a dust-free region inside the dust cloud. This occurs under conditions relevant to both plasma processing discharges and plasma crystal experiments. The void results from a balance of the electrostatic and ion drag forces on a dust particle. The ion drag force is driven by a flow of ions outward from an ionization source and toward the surrounding dust cloud, which has a negative space charge. In equilibrium the force balance for dust particles requires that the boundary with the dust cloud be sharp, provided that the particles are cold and monodispersive. Numerical solutions of the one-dimensional nonlinear fluid equations are carried out including dust charging and dust-neutral collisions, but not ion-neutral collisions. The regions of parameter space that allow stable void equilibria are identified. There is a minimum ionization rate that can sustain a void. Spatial profiles of plasma parameters in the void are reported. In the absence of ion-neutral collisions, the ion flow enters the dust cloud's edge at Mach number M=1. Phase diagrams for expanding or contracting voids reveal a stationary point corresponding to a single stable equilibrium void size, provided the ionization rate is constant. Large voids contract and small voids expand until they attain this stationary void size. On the other hand, if the ionization rate is not constant, the void size can oscillate. Results are compared to recent laboratory and microgravity experiments.

Peptidyl transferase center activity observed in single ribosomes

We demonstrate the functional activity of single ribosomal complexes, opening the way for detailed studies of the trajectories of protein synthesis. Our approach employs a single-molecule detection system, capable of picoseconds to minutes resolution, to observe a growing peptide labeled at its N terminus with the fluorophore tetramethylrhodamine (TMR). Single complexes of mRNA-programmed ribosomes with TMR-Met-tRNAMetf or TMR-Met-Phe-tRNAPhe are immobilized on mica and observed by fluorescence. Immobilized ribosome.mRNA.TMR-Met-tRNAMetf complexes form peptide bonds with puromycin. Single-molecule detection reveals dynamics on the scale of seconds at the ribosomal peptidyl transferase center.

Three-dimensional placement of the conserved 530 loop of 16 S rRNA and of its neighboring components in the 30 S subunit

Nucleotides 518-533 form a loop in ribosomal 30 S subunits that is almost universally conserved. Both biochemical and genetic evidence clearly implicate the 530 loop in ribosomal function, with respect both to the accuracy control mechanism and to tRNA binding. Here, building on earlier work, we identify proteins and nucleotides (or limited sequences) site-specifically photolabeled by radioactive photolabile oligoDNA probes targeted toward the 530 loop of 30 S subunits. The probes we employ are complementary to 16 S rRNA nucleotides 517-527, and have aryl azides attached to nucleotides complementary to nucleotides 518, 522, and 525-527, positioning the photogenerated nitrene a maximum of 19-26 A from the complemented rRNA base. The crosslinks obtained are used as constraints to revise an earlier model of 30 S structure, using the YAMMP molecular modeling package, and to place the 530 loop region within that structure.

Dynamics of two particles in a plasma sheath

The stability and arrangements of two dust particles in a plasma are investigated in terms of the Hamiltonian of the system. It is shown that the Hamiltonian description of a non-Hamiltonian system can be used to predict qualitative features of possible equilibria in a variety of confinement potentials and can provide useful plasma diagnostics. The results compare favorably with those of simulations and are used to create experimental hypotheses. In particular, the symmetry-breaking transition of the particles as they leave the horizontal plane admits a Hamiltonian description which is used to elucidate the wake parameters.

Development of the suprachiasmatic nucleus in rats during ontogenesis: serotonin-immunopositive fibers

The innervation of the suprachiasmatic nucleus by serotoninergic fibers has been studied in rats from the 22nd embryonic until the 21st postnatal day. The serotoninergic fibers were detected with the pre-embedding immunocytochemical technique at the electron-microscopic level using antibodies to serotonin. Serotonin-immunopositive fibers were always identified as axons as they contained numerous synaptic vesicles both in fetuses and postnatal rats. Moreover, immunopositive dense core vesicles appeared in the axons after birth. From the end of fetal life onwards, the serotonin-immunopositive axons made specialized contacts with the immunonegative neurons, mainly with their dendrites and to a lesser extent with cell bodies and axons. In fetuses, only immature synapses (presynapses) were observed. After birth, presynapses were replaced by typical synapses with the thickened pre- and postsynaptic membranes, accumulations of dense materials at the pre- and postsynaptic membranes as well as with an accumulation of synaptic vesicles at the presynaptic membrane. The functional significance of the serotoninergic input to the suprachiasmatic nucleus in ontogenesis is discussed.

HPTLC assay of cephalexin and cefaclor in pharmaceuticals

A simple and reliable HPTLC method for the simultaneous determination of cephalexin and cefaclor is developed and validated. The methanol-ethyl acetate-acetone-water (5:2.5:2.5:1.5 v/v/v/v) solvent system is used for the quantitative evaluation of chromatograms. The chromatographic zones, corresponding to the spots of cephalexin and cefaclor on the silica gel plates, are scanned in the reflectance/absorbance mode at 265 nm. The method is found to be reproducible and convenient for the quantitative analysis of cephalexin and cefaclor in its dosage forms.

Development of the suprachiasmatic nucleus in rats during ontogenesis: tyrosine hydroxylase immunopositive cell bodies and fibers

This study has evaluated differentiation of tyrosine hydroxylase-immunopositive neurons in the suprachiasmatic nucleus as well as the innervation of this nucleus by tyrosine hydroxylase-immunopositive axons in rats during ontogenesis. Tyrosine hydroxylase-containing structures were detected with electron-microscopic pre-embedding immunocytochemistry at the 22nd fetal day as well as at the second, ninth and 21st postnatal days. Rare uni- and bipolar small tyrosine-hydroxylase-immunopositive neurons were observed in the suprachiasmatic nucleus both in fetuses and postnatal rats. These neurons underwent differentiation over the perinatal period that was mainly manifested in the increase of their size as well as in the development of the Golgi complex, granular endoplasmic reticulum and the onset of the dense core vesicle production. Concomitantly, tyrosine hydroxylase-immunopositive neurons, cell bodies and dendrites, became innervated by immunonegative axons first making presynapses, and, then, symmetric (Gray-type II) and asymmetric (Gray-type I) synapses. In addition to cell bodies and dendrites, tyrosine hydroxylase-immunopositive axons were regularly observed in ventral, ventrolateral and ventromedial regions of the suprachiasmatic nucleus in fetuses and postnatal rats. Tyrosine hydroxylase-immunopositive axons were observed either in simple appositions with the immunonegative neurons or making presynapses in fetuses and symmetric and asymmetric synapses in postnatal animals. The nature of the tyrosine hydroxylase-immunopositive axons and the functional significance in the suprachiasmatic nucleus in ontogenesis are discussed.

Determination of some insect repellents in cosmetic products by high-performance thin-layer chromatography

A simple and reliable thin-layer chromatographic method for the determination of N,N-diethyl-m-toluamide (DEET) and dimethyl phthalate (DMP) in raw material and cosmetic products was developed and validated. A benzene-diethyl ether-cyclohexane (5:3:2, v/v/v) solvent system was used for quantitative evaluation of chromatograms. The chromatographic zones corresponding to the spots of DEET and DMP on the silica gel plates were scanned in the reflectance/absorbance mode at 230 nm. The method was found to be reproducible and convenient for the quantitative analysis of DEET and DMF in raw material and cosmetic products.

Simultaneous HPLC determination of nitrendipine and impurities of the process of synthesis

A method has been developed for separation of nitrendipine and its impurities of reaction partners and side reaction products by high-performance liquid chromatographic method on a RP-18 column and detection at 238 nm. The mobile phase composition that provided an acceptable nitrendipine resolution, in large excess and possible impurities, in a short elution time, is methanol:water (70:30) and pH 3. Linearity (r> or =0.999), reproducibility (RSD=0.8--1.4%), determination limit (0.5--2%) and recovery (99.8--102.3) were validated and found to be satisfactory. This method enables monitoring of the process of synthesis, as well as the choice of the synthetic design.

Electromagnetic wave band structure due to surface plasmon resonances in a complex plasma

The dielectric properties of complex plasma containing either metal or dielectric spherical inclusions (macroparticles, dust) are investigated. We focus on surface plasmon resonances on the macroparticle surfaces and their effect on electromagnetic wave propagation. It is demonstrated that the presence of surface plasmon oscillations can significantly modify plasma electromagnetic properties by resonances and cutoffs in the effective permittivity. This leads to related branches of electromagnetic waves and to the wave band gaps. The conditions necessary to observe the band-gap structure in laboratory dusty plasma and/or space (cosmic) dusty plasmas are discussed.

Densitometric determination of conjugated oestrogens in the raw material and in pharmaceutical preparations

A densitometric method for determination of complex mixtures of conjugated oestrogens in raw material and tablets was developed. The proposed procedure comprised hydrolysis of sodium sulphate esters of oestrone, equilin, 17 alpha-oestradiol, equilenin, 17 alpha-dihydroequilin and 17 alpha-dihydroequilenin, the chloroform extraction of free oestrogens and methyltestosterone (internal standard) and separation on TLC plates using chloroform-cyclohexane-dioxane-triethylamine (4.5:4.1:0.6, v/v) as the solvent for development. Quantitative assay was achieved by direct scanning of the oestrogen spots at 280 nm. The proposed method is simple, rapid, reproducible and adequate to control the content of conjugated oestrogens in the raw material and in pharmaceutical preparations.

Effects of Electrospinning Parameter Adjustment on the Mechanical Behavior of Poly-ε-caprolactone Vascular Scaffolds

Electrospinning is a perspective method widely suggested for use in bioengineering applications, but the variability in currently available data and equipment necessitates additional research to ascertain the desirable methodology. In this study, we aimed to describe the effects of electrospinning technique alterations on the structural and mechanical properties of (1,7)-polyoxepan-2-one (poly-ε-caprolactone, PCL) scaffolds, such as circumferential and longitudinal stress/strain curves, in comparison with corresponding properties of fresh rat aorta samples. Scaffolds manufactured under different electrospinning modes were analyzed and evaluated using scanning electronic microscopy as well as uniaxial longitudinal and circumferential tensile tests. Fiber diameter was shown to be the most crucial characteristic of the scaffold, correlating with its mechanical properties.

Criteria of phase transitions in a complex plasma

New empirical rules for different phase transitions (including the melting of cubic lattices and the transitions between body-centered-cubic and face-centered-cubic structures) are proposed. The arrangements of charged macroparticles in a complex "dusty" plasma are numerically investigated for the conditions of laboratory experiments on weakly ionized gas discharges.

Spectrophotometric determination of desoximetasone in ointment using 1,4-dihydrazinophthalazine

The proposed method is based on coloured hydrazone formation with 1,4-dihydrazinophthalazine as a reagent. Heating at 85 degrees C for 2 h was found necessary to ensure optimal hydrazone formation in the presence of hydrochloric acid. The yellow hydrazone product has an absorption maximum at 380 nm. A linear relationship between absorbance and concentration was established in the concentration range 3.19 x 10(-6) -3.19 x 10(-5) mol l-1 (the regression equation was y = 0.013 167 3 + 0.019 025 9x; correlation coefficient r = 0.9991; n = 6). The detection limit was 1.2 micrograms ml-1 (molar absorptivity found was 1.97 x 10(4) l mol-1 cm-1). The reliability of the proposed method was checked at three different concentrations; the relative standard deviation (RSD) varied from 1.03 to 2.01%. The described method applied to the determination of desoximetasone in ointment gave precise and reproducible results; the recovery was 98.55% with RSD = 2.40% (n = 10).